1. Field of the Invention
The present invention relates to a continuous liquid infusion device, and particularly to a continuous liquid infusion device which is simply preparable for operation with small force, easy to handle, and capable of infusing liquid at a predetermined infusion rate and amount over a long period of time.
2. Description of the Related Art
In infusing liquid for treatment into human or animal bodies, liquid is continuously infused at a predetermined flow rate for a long time in some cases. For example, there are cases which require transfusion of a nutrition supplement solution or the like, or liquid infusion such as an anticoagulant compound, an anticancer compound, a demulcent, a local anesthesia compound, a blood sugar value adjusting compound, or the like in a solution state into a body of a patient from his/her vein, artery, hypodermis, epidural space, or the like at a predetermined flow rate over a long time.
In such cases, an infusion device using an electric syringe pump, an infusion device (balloon infuser) which performs infusion through the use of contraction force of a balloon having elasticity, an infusion device utilizing elasticity of a spring, and so on are conventionally used.
However, the infusion device using the electric syringe pump described above has a large weight and is inconvenient for the patient to carry when he/she moves as well as it is complicatedly structured and expensive. Further, since the balloon infuser does not have constant contraction force of the balloon and liquid discharging force, it is difficult to continuously infuse liquid at a constant flow rate so liquid sometimes remains in the balloon. Furthermore, with these conventional infusion devices driven by the balloon or the spring, it is difficult to maintain precision of the predetermined infusion rate and amount of liquid over a long time.
Accordingly, proposed is a liquid infusion device in which a second cylinder internally maintained under negative pressure by operation of a piston or the like is mounted on a first cylinder filled with liquid, and the liquid in the first cylinder is pushed out by the piston which is driven by negative pressure in the second cylinder (Japanese Utility Model Laid-open No. Hei 5-20751, Japanese Patent Laid-open No. Hei 5-176997, and International Publication No. WO95/28977).
However, these conventional infusion devices utilizing negative pressure are not easy to handle because they need large force for operating the piston or the like to form negative pressure. For example, the piston is slidably inserted and fitted into a center barrel which is inserted in the center of the second cylinder, and hence sliding resistance due to an air-tight holding member such as an O-ring, which is arranged between the center barrel and the piston for inserting and fitting the piston into the center barrel air-tightly, is large or leakage or the like of air is prevented in forming negative pressure in the second cylinder at the same time of infusing liquid, which requires large force when the piston is pushed up.
Moreover, since the infusion devices have the particular structure such as the center barrel provided in the second cylinder, they need to be handled with caution and their manufacturing cost is high.
Furthermore, it is difficult to maintain negative pressure, which is driving force for infusion, constant over a long time and there is a problem in precision of an infusion rate and amount of liquid.
An object of the present invention is to provide a continuous liquid infusion device capable of infusing liquid into a liquid syringe with smaller force compared with that required for the conventional liquid infusion device utilizing negative pressure, preparable for operation with small force by a small driving pump section, and facilitating intra-arterial infusion requiring pressure of 300 mmHg or more. Further, it is another object of the present invention to provide a continuous liquid infusion device which is simply structured and easy to handle, in which a liquid syringe section and a driving pump section are separable, and which is advantageous in terms of cost, whose leakage of air and sliding resistance are not too large, and which is capable of performing infusion at a constant infusion rate and liquid amount and is excellent in durability.
In order to solve the aforementioned problem, the present invention provides a continuous liquid infusion device comprising a liquid syringe section and a driving pump section mounted on the liquid syringe section. The liquid syringe section has a liquid infusion port at one end, an opening at the other end connected with a bottom end part of the driving pump section, a liquid filling chamber in communication with the liquid infusion port, and a pushing member including a peripheral edge in sliding contact with an inner circumferential wall of the liquid filling chamber and being slidable due to the peripheral edge to reciprocate air-tightly and liquid-tightly in an axis direction of the liquid syringe section. The driving pump section has a liquid pushout plunger barrel including the bottom end part abutting on an upper edge of the pushing member and at least two pressing arms connected to the bottom end part and inserted and fitted into the liquid filling chamber along the inner circumferential wall, and an internal negative pressure cylinder to be inserted and fitted into the liquid pushout plunger barrel, including a negative pressure chamber therein, and having a piston inserted and fitted thereinto, for producing negative pressure by sliding in the axis direction in the negative pressure chamber air-tightly. In the continuous liquid infusion device, sliding the pressing arms of the driving pump section toward an upper end causes the piston to slide and be pushed up in the negative pressure chamber in the axis direction to produce negative pressure in the negative pressure chamber, and the liquid pushout plunger barrel is biased toward the upper edge of the pushing member via a locking member engaged with the piston by utilizing returning force of the piston due to the negative pressure so that the biased pushing member pushes liquid in the liquid syringe out of the liquid infusion port.
According to another aspect of the present invention, provided is the continuous liquid infusion device characterized in that the liquid syringe section and the driving pump section are structured to be separable.
Further, according to still another aspect of the present invention, provided is the continuous liquid infusion device characterized in that the liquid syringe section is structured of a plurality of auxiliary syringe parts and has pressing arms and bottom end parts corresponding to the respective pushing members, the pressing members being to be inserted and fitted into the plurality of auxiliary syringe parts.
Furthermore, according to yet another aspect of the present invention, provided is a continuous liquid infusion device which comprises: a first structure having a vacuum pump barrel which includes an open/close valve at its front end and an open rear end, a piston fitted into the vacuum pump barrel air-tightly, a stopper capable of locking the piston at the rear end of the vacuum pump barrel against atmospheric pressure, and a pusher movable in the same direction as that of the piston outside the vacuum pump barrel; and a second structure having a liquid syringe which includes a liquid port at its front end and an open rear end, and a piston fitted into the liquid syringe liquid-tightly, wherein the first structure and the second structure are removably connected.
Moreover, according to yet another aspect of the present invention, provided is the continuous liquid infusion device characterized in that the first structure and the second structure are connectable in a state in which the front end of the vacuum pump barrel of the first structure extends further forward than the front end of the liquid syringe.
Further, according to yet another aspect of the present invention, provided is the continuous liquid infusion device characterized in that the first structure has dual pushers and the second structure has dual liquid syringes.
As described above, the continuous liquid infusion device according to the present invention is structured to bias the liquid pushout plunger barrel via the locking member engaged with the piston and push out liquid in the liquid syringe by utilizing returning force of the piston due to negative pressure inside the vacuum pump barrel, which enables liquid infusion at constant infusion rate and amount over a long period of time and easy handling, and brings about an advantage in terms of cost.